A generally-available pulse radar apparatus includes a radio frequency transmission unit that generates a pulse-shape transmission signal by gating a carrier frequency for a very short period of time by modulating a carrier wave of a radio frequency, a transmission antenna that radiates the transmission signal generated by the radio frequency transmission unit as a radio wave into the space, a reception antenna that receives a reflected wave which the radio wave emitted from the transmission antenna reflected and returned back from a target, a radio frequency reception unit that receives a reception signal from the reception antenna and down-converts the reception signal into a baseband signal, and a baseband unit that receives the baseband signal from the radio frequency reception unit and calculates the distance and the like to the target.
The radio frequency transmission unit includes an oscillation apparatus that generates a carrier wave of a predetermined frequency and a switch and the like for gating the carrier wave generated by the oscillation apparatus into a pulse-shape. The radio frequency reception unit includes a correlation apparatus that obtains correlation between the transmission signal and the reception signal and an IQ mixer that down-converts the output signal of the correlation apparatus into a baseband signal. The baseband unit includes an A/D conversion unit that converts the baseband signal given by the radio frequency reception unit from analog signal into digital signal, a digital signal processing unit that processes the digital signal provided by the A/D conversion unit to calculate the relative speed of the target and the distance to the target, and a control unit that controls the pulse radar apparatus. The control unit controls the ON/OFF state of the correlation apparatus of the radio frequency reception unit and the switch of the radio frequency transmission unit.
As explained above, the pulse radar apparatus includes the radio frequency transmission unit and the radio frequency reception unit that process the radio frequency signal (hereinafter, both of which will be collectively referred to as RF unit) and the baseband unit that processes a low frequency signal. Among them, the RF unit needs to use an expensive circuit board capable of supporting a radio frequency, and therefore, conventionally, in order to reduce the cost, only the RF unit is usually provided on the circuit board capable of supporting the radio frequency, and the baseband unit is usually provided on a less expensive circuit board. A small and inexpensive multi-pin connector has been conventionally used as means for connecting the RF unit with the baseband unit provided on separate circuit boards.
As described above, when the baseband unit and the RF unit formed on separate circuit boards are connected to each other by a cheap and integrated multi-pin connector, there is a problem in that the control signal leaks into the reception signal as an interference noise signal. As described above, when an undesired wave such as the control signal generated secondarily in the multi-pin connector leaks into the reception signal to make the interference noise signal, and a sufficient level of reception strength cannot be obtained, there is a problem in that the desired reception signal is buried in the interference noise signal. Therefore, the amount of signal of the interference noise signal is conventionally reduced by increasing isolation between the multiple pins as much as possible, so as to allow detection of a reception signal having a low reception strength.
Such an interference noise signal exists in various kinds of radar apparatuses although the cause of occurrence is different, and there is a technique for removing the interference noise signal. Patent Literature 1 discloses an interference noise signal reduction processing for a steady-state noise component overlaid on a reception signal (component of which changes of frequency and level are low in terms of time) in an FM-CW radar. The steady-state noise component is memorized, and it is subtracted from the spectrum distribution of the reception signal, whereby a target is detected.
Patent Literature 2 discloses a technique for detecting a target with a high degree of accuracy by obtaining, as a replica signal, an interference noise signal, a self mixing noise, and the like of the pulse radar apparatus, and removing them from observation data.